The vagus nerve has long been known to play a role in the regulation of food intake. The vagal afferent pathway senses hormones released from the gut in response to nutritional cues and relays these signals to the brain stem. We have recently demonstrated that vagal afferent neurons (VAN) can integrate these signals and alter expression of receptors and neuropeptide transmitters important in sensing and signalling, to modify feeding behavior. In obesity, the sensitivity of key receptors to their ligands are reduced in VAN, resulting in changes in the neurochemical phenotype of these neurons. Unfortunately the techniques currently available in the field do not allow manipulations of these neurons in vivo to determine the functional role of these proteins on feeding behavior. The overarching goal of this proposal will be to determine the role of the vagus nerve in regulating feeding behaviour with specific focus on understanding how dysregulation of vagal afferent signaling leads to the development of hyperphagia and weight gain in diet induced obesity. To achieve this goal we propose to 1) determine the role of the neuropeptide transmitters cocaine and amphetamine regulated transcript (CART), and melanin concentrating hormone (MCH) released from VAN into the brain stem in the regulation of feeding behavior under normal physiological conditions and their role in the progression of diet induced obesity, 2) the effect of leptin resistance in VAN on the progression of obesity, and 3) to use an intervention study targeting MCH and the leptin receptor downstream effector early growth response 1 (EGR-1) to prevent the onset of diet induced obesity. A key component of this proposal involves the development of a novel in vivo RNAi approach to target proteins expressed by VAN. The expected outcomes of this research proposal are to develop a novel in vivo RNAi approach to target proteins expressed by VAN and to demonstrate that this technique could be applied as a therapeutic tool in obesity as well as a research tool to elucidate the role of VAN. In addition, successful completion would demonstrate an important role for VAN in the development hyperphagia and weight gain; thereby identifying novel specific molecular targets for the treatment of obesity.